The present invention relates in general to an electron beam scanning device and more particularly to a metal-dielectric electron beam scanning stack and method for making the same.
This application is filed on even date with another copending patent application by William Gary Manns and also assigned to Texas Instruments Incorporated, the same assignee of the present patent application. Both of these inventions relate to the fabrication of a metal-dielectric electron beam scanning device. The invention of the present application eliminates the need for using spacer plates in the manufacture of the subassemblies, thus reducing the number of plates per flat tube display and a reduction in its associated manufacturing cost.
Present flat tube displays are fabricated from glass switching plates and glass spacer plates. Each plate is provided with a matrix of apertures therein fabricated by a chemical etching technique. In fabricating a matrix of apertures in the glass plates, etching masks of precious metals, for example, platinum, gold and titanium are employed to protect selected planar surfaces of the glass plates from the etchant solutions. Upon completion of the etch process, these precious metals are stripped and recovered by standard refining techniques.
The switching plates are coated on both sides and through the aperture holes with a metallized thin-film employing standard techniques. This metallized thin-film is patterned into an appropriate switching matrix using either a conventional photolithographic metal-etching technique or standard photoresist lift-off techniques.
Gold ribbon leads are reflow solder bonded to metallized bonding pads located on each of the switching plates corresponding to each switching matrix pattern. The glass spacer plates are coated with solder glass-frit and the plates assembled into a switching stack array using a thermal solder glass-frit firing cycle and aperture alignment fixtures. These switching stacks thereby comprise alternate layers of glass switching plates and glass insulating plates. The matrix array of aligned apertures in the glass plates provides electron beam channels to the phosphor coated screen. The gold leads are bonded to a mounting plate during the assembly providing for the external electronic circuit connections.
These glass stacks are mechanically fragile, expensive to fabricate, and are frequently broken by thermal stresses during fabrication and operation. In addition, dangerous chemical etching systems used for the glass etching require very expensive processing equipment for adequate operating safety. As noted above, the glass etching process requires expensive precious metal masking in addition to the standard photoresist masking. The low thermal conductivity of the glass switching plates and spacers results in excessive stack heating during high stack input currents that are required for high brightness displays. Finally, thin-film metal deposition processes require vacuum metal applications that increase costs due to the use of multiple vacuum process steps. Other nonvacuum deposition processes have not been successfully demonstrated for switching stack fabrication.